In recent years, as computers have developed and become popular, various kinds of information are put into digital data. As a device for storing such digital data, there is a storage device such as a magnetic tape and a magnetic disk. Because data to be stored has increased day by day and the amount thereof has become huge, a high-capacity storage system is required. Moreover, it is required to keep reliability while reducing the cost for storage devices. In addition, it is required that data can be easily retrieved later. As a result, such a storage system is desired that is capable of automatically realizing increase of the storage capacity and performance thereof, that eliminates a duplicate of storage to reduce the cost for storage, and that has high redundancy.
Under such circumstances, in recent years, a content address storage system has been developed as shown in Patent Document 1. This content address storage system distributes data and stores into a plurality of storage devices, and specifies a storing position in which the data is stored based on a unique content address specified corresponding to the content of the data.
To be specific, in the content address storage system, as shown in FIG. 1, a division unit 101 of a storage server 100 divides a data block that is storage target data into a plurality of fragments, and also adds a fragment that is redundant data thereto. Then, the division unit 101 stores the plurality of fragments into a plurality of storage devices such as a storage device 102 within the storage server 100 and storage devices 103 and 104 included in other storage servers. Later, by designating a content address, it is possible to retrieve data, namely, a fragment stored in a storing position specified by the content address and restore predetermined data before divided from the plurality of fragments.
Further, the content address is generated so as to be unique corresponding to the content of data. Therefore, in the case of duplicated data, it is possible to acquire data having the same content with reference to data in the same storing position. Thus, it is not necessary to separately store duplicated data, and it is possible to eliminate duplicated recording and reduce the data capacity.
Then, in the case of writing two or more pieces of fragment data (referred to as a “fragment” hereinafter) divided from one data block into one server, in order to keep the tolerance to disk fault, the storage system as described above distributes and stores the two or more fragments into the respective disks so as not to write the two or more fragments into one disk. On the other hand, when it is necessary to write two or more fragments that belong to different data blocks into one disk, the storage system makes a queue of the fragments waiting for being written and then writes in. The storage system executes a process of writing the fragment or the fragments from the queue into the disk by transaction processing, and records data representing a status of the transaction processing as a journal.
FIG. 2 shows an aspect of storing the status of the transaction processing described above as a journal. As shown in this drawing, a journal (J) is configured by a start entry written immediately before the writing of data (D) starts, a commit entry written immediately after the writing of the data ends, and a deletion entry for the used start/commit entries.
Then, for keeping redundancy, a journal 110 as described above is fixedly placed within OS (Operating System) regions 120 of disk regions configuring hardware RAID (Redundant Arrays of Inexpensive Disks) as shown in FIG. 3. In other words, the journal is placed within the OS regions 120 duplicated in two disks. As a related art, Patent Document 2 describes a technique of switching a file for storing a journal when a space for storing the journal is not available any more.
On the other hand, in order to maximize the utilization of a disk capacity, it is necessary to use each of the remaining capacities of the disks (disk 0, disk 1) including the OS regions 120 as a data region 130. This is critically important because an OS region is relatively small in a disk, which has become high-capacity nowadays. Therefore, it is necessary to provide a disk including the OS region 120 and other disks, namely, all disks (disk 0 to disk n) with data regions 130 for storing data.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. JP-A 2005-235171    [Patent Document 2] Japanese Unexamined Patent Application Publication No. JP-A 1990-54346
However, in the case of distributing and storing storage target data like fragment data into the disks having the OS regions 120 as well, there is a problem that the writing performance of the storage system decreases. To be specific, as shown in FIG. 4, in a case that fragment data are stored into the disks having the OS regions, the fragment data and the journal are stored into the same disks (disk 0 and disk 1). This causes contention of the writing process in the disks, delays the writing, and delays completion of the writing of the original data block having been fragmented. As a result, the problem of decrease of the writing performance arises. Moreover, in the event of a disk failure, both the data and the journal may be lost, and therefore, a problem of decrease of reliability also arises.